Today, laser technology is widely used in dermatologic, aesthetic medicine, and professional aesthetic treatments. The laser removal of hair is one among the possible treatments, one of the most widely used worldwide. The concept on which it is based is selective photothermolysis. By selecting a laser with the proper wavelength and energy per surface unit (fluency), a particular target substance present in the light-absorbing tissue (chromophore), such as, for example, melanin or hemoglobin, absorbs the laser beam energy so as to be heated such that the function of the tissue containing the chromophore is destroyed. The tissues which are present in the same area which do not have a high concentration of target chromophore will be not affected. For example, during epilation, a laser emits a monochromatic light at a predetermined fluency, so as to selectively hit the melanin present in the hair bulb, thus destroying it (R. G. Wheland, “Laser-assisted hair removal”, Lasers in Dermatology, Vol. 15, pp. 469-477). Hair are composed of two major parts: the shaft, i.e., the hair portion above the epidermis, and the root, that is the portion below the epidermis surface. Various tissues surround the hair roots. The hair color is mainly due to the presence of melanin. Melanin is produced at the base of the hair follicle. It is exactly the presence of melanin that made the use of the laser for the epilation possible, where melanin acts as a target chromophore and, since it is located at the base of the hair follicle, with the heating due to the laser it damages the hair follicle itself.
Other dermatologic and aesthetic medicine treatments in which the laser technology finds wide application are the face and body vascular treatments, among which, by way of non-exhaustive example, the removal of telangectasias, erythroses, red and blue capillaries, angiomas, varicose veins are noted; treatments of face and body pigmented lesions, among which, by way of non-exhaustive example, removal of tattoos, skin stains, melasmas, melanomas, skin moles; resurfacing, non-ablative or ablative photorejuvenation treatments, peeling, dermatologic treatment of skin imperfections to be treated surgically and non-surgically, for example, the treatment of scars in general, including post-acne scars, keloids, condylomata, fibromas; the treatments of psoriasis and vitiligo are noted.
Among the various classes of lasers that are used, i) diode lasers; ii) lamp-pumped lasers are distinguished.
In diode lasers, the source is composed of power emitting diodes that are assembled to one another to form a diode block, so-called stacks, so as to obtain a high overall power, currently up to 4,000 W. This energy is emitted with a very high divergence, and it is generally collected by “optical funnels”, i.e., light guides collecting the energy and transporting it onto a small, generally rectangular area. These guides are usually of sapphire.
In the lamp-pumped lasers, a crystal rod, referred to as an active medium, is excited by a lamp with short, intense pulses, thus emitting energy for the time corresponding to the turn-on period of the lamp. The lamp-pumped lasers do not emit continuously, as the case is instead for the diode laser, but with pulses having a peak power up to some GWs and with a duration of the order of milliseconds, microseconds, or even nanoseconds. In the lamp-pumped systems, the laser beam emitted by the crystal is conveyed with a lens system in an optical fibre which has the function of transporting the energy. The use of fibers allows the operator working also at a distance of meters from the source, without particular losses of energy during transportation. In some cases, when the source is inserted in a handpiece, the energy is transported also by light guides, but with a high dispersion of energy and a worsening of the quality of the beam.
The optical fibres currently used in the laser systems applied to dermocosmesis, medicine, and aesthetic treatments are optical fibres having a circular section, typically coupled to a handpiece projecting in output the image located at the inlet of the handpiece, so that the dimension of the image in output can be adjusted by the user. Circular images in input will result in output images which are again circular, but of different dimensions.
During the treatment, it is necessary to expose to the energy laser in a complete and even manner the area of tissue at issue, and the circular shape of the image in output is a major obstacole. Circular-shaped spots arranged side by side cannot allow a complete covering of the area of interest without being superimposed. The superimposition creates energy overexposures, with the consequent risk of burns. Having to avoid the superimposition, it is inevitable that there are untreated, uncovered areas, which require a further treatment to be performed in a successive moment.
A further drawback deriving from the use of circular-shaped spots is the fact that the energy is distributed in a Gaussian manner onto the circular spot, with a maximum intensity peak at the centre of the area. These localized densities increase the risk of undesired microburns at the centre of the spot, and make the energy on the perimeter of the spot itself insufficient.
The need is strongly felt, to provide devices for dermocosmetic, medical, or aesthetic laser treatments which allow an homogeneous treatment of the area to be treated, avoiding the risks related to superimpositions and to areas in which a higher density of energy is concentrated, in addition to the drawbacks related to the failed treatment of some areas.